Insulation monitoring device to reduce measurement error of insulation resistance

Abstract

An insulation monitoring device according to one disclosed embodiment is an insulation monitoring device for monitoring the insulation status of one or more power lines, comprising: a signal generator that generates a test signal applied to the one or more power lines; a signal detector that measures a detection signal returning after the test signal passes through the one or more power lines; and a signal processor that calculates a composite insulation resistance representing the overall insulation status of the one or more power lines based on the test signal, the detection signal, and one or more internal resistances constituting the insulation monitoring device.

Description

Technology Field

[0001] An embodiment of the present invention relates to an insulation monitoring device. Background Technology

[0003] Among electrical grounding systems, there is an insulation monitoring device in the primary insulation section of the low-voltage distribution system IT (Insulation Terra) grounding system to prevent electric shock and fire accidents caused by insulation breakdown.

[0004] Isolated Terra (IT) grounding is a method in which neither end of the power line is grounded, and only the load enclosure is grounded. The primary reason for using this grounding method is the advantage of ensuring continuous operation without halting system operation, even if a fault occurs on one side of the power line. However, to obtain this advantage, it is necessary to continuously monitor the condition of the system's power lines using an insulation monitoring device. To continuously monitor the condition of the system's power lines, the calculated value of insulation resistance (Re) must be monitored using an insulation monitoring device. The insulation monitoring device for power line condition monitoring complies with the standards of IEC 61557.

[0005] If the insulation resistance of power lines is not maintained and decreases, it can lead to economic losses such as equipment failure, electric shock, and fire accidents; therefore, the development of an insulation monitoring device that accurately measures insulation resistance is required.

[0006] Figure 1 is a graph illustrating the error that occurs when measuring insulation resistance in a conventional insulation monitoring device.

[0007] Referring to FIG. 1, the measured value and the theoretical value of the voltage across the detection resistor, which is measured to monitor the insulation status of a power line, may differ. Specifically, the insulation monitoring device may send a test signal to the power line to verify the insulation status and receive the test signal passing through the power line to use as a detection signal. At this time, the physical form of the test signal and the detection signal may be voltage. The insulation monitoring device can calculate the insulation resistance, which indicates the insulation status, from the voltage of the detection signal.

[0008] In other words, the fact that the measured value of the detection signal measured by the insulation monitoring device differs from the theoretical value may mean that the measured value of the insulation resistance, which indicates the insulation status of the power line, differs from the theoretical value.

[0009] Accordingly, an insulation resistance measuring device is required to provide an insulation resistance value by correcting the calibration value for error-causing factors. Prior art literature

[0011] Korean Patent Publication No. 10-2307773 (September 27, 2021) The problem to be solved

[0012] The objective of the present invention is to provide an insulation monitoring device capable of measuring an accurate resistance value by taking into account errors caused by the physical structure of the measuring device when measuring insulation resistance.

[0013] The objects of the present invention are not limited to those mentioned above, and other objects and advantages of this specification not mentioned may be understood from the following description and will be more clearly understood by the embodiments of this specification. Furthermore, it will be readily apparent that the objects and advantages of this specification can be realized by the means and combinations thereof set forth in the claims. means of solving the problem

[0015] An insulation monitoring device according to one disclosed embodiment is an insulation monitoring device for monitoring the insulation status of one or more power lines, comprising: a signal generator that generates a test signal applied to the one or more power lines; a signal detector that measures a detection signal returning after the test signal passes through the one or more power lines; and a signal processor that calculates a composite insulation resistance representing the overall insulation status of the one or more power lines based on the test signal, the detection signal, and one or more internal resistances constituting the insulation monitoring device.

[0016] The signal processor can obtain a composite insulation resistance before correction based on the test signal, the detection signal, and a detection resistor for measuring the detection signal, obtain a theoretical composite insulation resistance based on the test signal, the detection signal, the detection resistor, and a coupler resistor for receiving the test signal, and obtain a calibration factor for correcting the measurement error of the insulation monitoring device based on the composite insulation resistance before correction and the theoretical composite insulation resistance.

[0017] The signal processor can calculate the calibration factor by dividing the theoretical composite insulation resistance by the composite insulation resistance before correction.

[0018] When the signal processor measures the composite insulation resistance after acquiring the calibration factor, it can acquire a corrected composite insulation resistance based on the composite insulation resistance before correction and the calibration factor.

[0019] The signal processor can calculate the corrected composite insulation resistance by multiplying the calibration factor by the composite insulation resistance before correction.

[0020] The insulation monitoring device further includes a signal coupler, and the signal coupler can maintain the insulation monitoring device in an insulated state from the one or more power lines and transmit the test signal that has passed through the one or more power lines to the signal detector.

[0021] The above signal coupler includes one or more coupler resistors, and the signal processor can calculate the composite insulation resistance by considering the coupler resistor as one of the internal resistances.

[0022] Each of the above one or more coupler resistors is connected in a one-to-one correspondence with the above one or more power lines, and the signal detector includes a detection resistor, and the detection signal may be a voltage across the ends of the detection resistor when the test signal passes through the power line, the coupler resistor, and the detection resistor.

[0023] The sum of the composite insulation resistance and the internal resistance may be inversely proportional to the detection signal and proportional to the test signal or the detection resistance.

[0024] The above composite insulation resistance ( ) can be equal to the following mathematical formula 1.

[0025] (Mathematical Formula 1)

[0026]

[0027] : Composite insulation resistance

[0028] : Test signal (applied voltage)

[0029] : Detector

[0030] : Detect signal (voltage across the terminals of the detection resistor)

[0031] : Combined resistance of coupler resistance and detector resistance

[0032] : Coupler resistor

[0033] Each of the above one or more power lines maintains an insulating state from the outside by means of an insulating resistance, and each of the above insulating resistances is connected in parallel to form the composite insulating resistance, and a decrease in the composite insulating resistance may indicate that one or more of the above one or more power lines have been insulatingly broken.

[0034] A method of operation of an insulation monitoring device according to another disclosed embodiment, in a method of operation of an insulation monitoring device for monitoring the insulation status of one or more power lines, comprises the steps of: generating a test signal applied to one or more power lines through a signal generator; measuring a detection signal that returns after the test signal passes through one or more power lines through a signal detector; and calculating a composite insulation resistance representing the overall insulation status of one or more power lines through a signal processor based on the test signal, the detection signal, and one or more internal resistances constituting the insulation monitoring device. Effects of the invention

[0036] According to one embodiment disclosed, when measuring insulation resistance, it is possible to measure an accurate resistance value by taking into account the error due to the physical structure of the measuring device.

[0037] By measuring insulation resistance precisely and accurately, human and material damage resulting from electric shock accidents, fire accidents, and equipment damage caused by insulation breakdown can be prevented. Brief explanation of the drawing

[0039] The present disclosure can be easily understood from the combination of the following detailed description and the accompanying drawings, where reference numerals denote structural elements. Figure 1 is a graph illustrating the error that occurs when measuring insulation resistance in a conventional insulation monitoring device. FIG. 2 is a drawing for explaining an insulation monitoring system according to one embodiment. FIG. 3 is a flowchart illustrating a method for an insulation monitoring device to measure composite insulation resistance according to one embodiment. FIG. 4 is a diagram illustrating the measurement of insulation resistance in an insulation monitoring device according to one embodiment. FIG. 5 is a block diagram illustrating a computing environment including a computing device suitable for use as an insulation monitoring device, according to one embodiment. Specific details for implementing the invention

[0040] Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The following detailed description is provided to facilitate a comprehensive understanding of the methods, apparatuses, and / or systems described herein. However, this is merely illustrative and the present invention is not limited thereto.

[0041] In describing the embodiments of the present invention, detailed descriptions of known technologies related to the present invention are omitted if it is determined that such detailed descriptions may unnecessarily obscure the essence of the present invention. Furthermore, the terms described below are defined in consideration of their functions within the present invention, and these may vary depending on the intentions or practices of the user or operator. Therefore, such definitions should be based on the content throughout this specification. Terms used in the detailed description are intended merely to describe the embodiments of the present invention and should not be limiting in any way. Unless explicitly stated otherwise, expressions in the singular form include the meaning of the plural form. In this description, expressions such as "include" or "comprise" are intended to refer to certain characteristics, numbers, steps, actions, elements, parts thereof, or combinations thereof, and should not be interpreted to exclude the existence or possibility of one or more other characteristics, numbers, steps, actions, elements, parts thereof, or combinations thereof other than those described.

[0042] Additionally, terms including ordinal numbers, such as 'first' or 'second', may be used to describe various components, but said components should not be limited by said terms. Such terms may be used for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be named the second component, and similarly, the second component may be named the first component.

[0043] Furthermore, when it is said that one configuration is "connected" to another configuration, this includes not only cases where they are "directly connected," but also cases where they are "connected with another configuration in between."

[0045] FIG. 2 is a drawing for explaining an insulation monitoring system according to one embodiment.

[0046] Referring to FIG. 2, the insulation monitoring system may include a power line (20) and an insulation monitoring device (100).

[0047] Each of the one or more power lines subject to monitoring by the insulation monitoring device (100) can maintain an insulating state from the outside by means of one-to-one corresponding insulation resistances (Re1 and Re2). Each insulation resistance (Re1 and Re2) can be connected in parallel with each other. The insulation monitoring device (100) can monitor the insulation state by measuring the composite insulation resistance (Re), which represents the overall insulation state of the one or more insulation resistances (Re1 and Re2) that maintain the insulating state. The composite insulation resistance may be the combined resistance of one or more insulation resistances connected in parallel.

[0048] The monitoring device (100) can monitor whether the insulation of the power line is being maintained or if the insulation is broken by analyzing the measured composite insulation resistance value. Specifically, if the composite insulation resistance decreases, it can be determined that one or more insulation resistances have been broken and current is leaking. The insulation monitoring device (100) can prevent damage such as electric shock accidents, fires, ground fault accidents, and equipment damage by providing an alarm when the composite insulation resistance (Re) decreases and opening the system through a switching relay.

[0049] The insulation monitoring device (100) may include a signal generator (110), a signal coupler (120), a signal detector (130), and a signal processor (140).

[0050] A signal generator (110) can generate a test signal and apply it to one or more power lines (20). The test signal can pass through one or more power lines (20) and an isolation impedance (Re,Ce) connected to each power line, then pass through a signal coupler (120) and be detected at a signal detector (130).

[0051] The detection signal measured by the signal detector (130) may be a signal after a voltage drop occurs due to the internal resistance included in the signal coupler (120) and the signal detector (130). At this time, the test signal generated by the signal generator (110) and the detection signal measured by the signal detector (130) may be a type of voltage.

[0052] A signal coupler (120) can be connected to protect the insulation monitoring device (100) from the high voltage of the power line (20) by keeping the insulation monitoring device (100) insulated from the power line (20). The signal coupler (120) can transmit the signal that has passed through the power line (20) and the insulation impedance (Re,Ce) connected to each power line to a signal detector (130). The signal coupler (120) may include a coupler resistor connected to each power line.

[0053] The insulation monitoring device (100) may not be able to accurately measure the composite insulation resistance (Re) due to the coupler resistance included in the signal coupler (120) and may measure a value containing an error. That is, the coupler resistance constituting the signal coupler (120) can act as the internal resistance of the insulation monitoring device (100) measuring the composite insulation resistance (Re).

[0054] A signal detector (130) can measure a detection signal that returns after a test signal passes through one or more power lines (20), an isolation impedance (Re, Ce) connected to each power line, and a signal coupler (120). The signal detector (130) may include a detection resistor and an amplifier.

[0055] The signal detector (130) can obtain a detection signal by measuring the voltage across the detection resistor and obtain an output signal by amplifying the detection signal through an amplifier. The signal detector (130) can transmit the output signal to a signal processor (140) to calculate a composite insulation resistance from the output signal.

[0056] The signal processor (140) may be composed of an ADC circuit for converting an output signal received from a signal detector (130) into a digital value, a signal controller for controlling a signal generator (110), and a circuit module for calculating a composite insulation resistance (Re) through a detection signal. At this time, the detection signal that serves as the basis for calculating the composite insulation resistance (Re) may be a type of voltage.

[0057] The signal processor (140) can correct the error caused by the coupler resistance included in the signal coupler (120) when calculating the composite insulation resistance (Re). The signal processor (140) can store the difference between the value corrected for the error caused by the coupler resistance and the raw measurement value without error correction as a calibration factor. In a measurement after storing the calibration factor, the signal processor (140) can provide the composite insulation resistance (Re) after adjusting the raw measurement value to the calibration factor.

[0059] According to the disclosed embodiment, when measuring insulation resistance, it is possible to measure an accurate resistance value by taking into account the error due to the physical structure of the measuring device.

[0060] By measuring insulation resistance precisely and accurately, human and material damage resulting from electric shock accidents, fire accidents, and equipment damage caused by insulation breakdown can be prevented.

[0062] FIG. 3 is a flowchart illustrating a method for an insulation monitoring device to measure composite insulation resistance according to one embodiment. The method illustrated in FIG. 3 may be performed, for example, by the insulation monitoring device (100) described above or the computing device (12) described below. Although the method is described in the illustrated flowchart in a plurality of steps, at least some of the steps may be performed in a different order, combined with other steps, omitted, divided into detailed steps, or performed with one or more steps not illustrated added.

[0063] Referring to FIG. 3, a method for measuring a composite insulation resistance representing the overall insulation state of one or more power lines by an insulation monitoring device (100) may include the steps of: generating a test signal applied to one or more power lines (S110); receiving a test signal that has passed through one or more power lines (S120); measuring a voltage across the two ends of a detection resistor as a detection signal when the received test signal passes through a detection resistor (S130); and calculating a composite insulation resistance representing the overall insulation state of one or more power lines based on the test signal and the detection signal (S140).

[0064] In step S110, the signal generator (110) can generate a test signal that is applied to one or more power lines. Specifically, the signal generator (110) can generate a voltage (hereinafter referred to as a test voltage) that is applied to a power line to check whether the current of the power line leaks outside the power line. The signal generator (110) can transmit (apply) the generated test signal to one or more power lines.

[0065] In step S120, the signal coupler (120) can receive a test signal that has passed through one or more power lines. Specifically, the signal coupler (120) can receive a test signal that has passed through components of a system including one or more power lines. At this time, since the path for the signal coupler (120) to receive the test signal is a physical component, it can act as a resistor (hereinafter referred to as a coupler resistor) that causes an error in measurement. The signal coupler (120) can transmit the test signal that has passed through the coupler resistor to the signal detector (130).

[0066] In step S130, the signal detector (130) can measure the voltage across the ends of the detection resistor as a detection signal when the input test signal passes through the detection resistor. Specifically, the signal detector (130) may include a resistor (hereinafter referred to as a detection resistor) for measuring composite insulation resistance, and can measure the voltage across the ends of the detection resistor as a detection signal when the test signal received from the signal coupler (120) passes through the detection resistor. The signal detector (130) can transmit the measured detection signal to the signal processor (140).

[0067] In step S140, the signal processor (140) can calculate a composite insulation resistance representing the overall insulation state of one or more power lines based on the test signal and the detection signal. Specifically, the signal processor (140) can calculate the composite insulation resistance based on the ratio of the test signal and the detection signal and the detection resistance. A more specific explanation regarding the calculation of the composite insulation resistance will be explained below with reference to FIG. 4.

[0068] In an exemplary embodiment, the signal processor (140) can calculate the composite insulation resistance before correction by ignoring the coupler resistance included in the signal coupler (120). Additionally, the signal processor (140) can calculate the theoretical composite insulation resistance by considering the coupler resistance included in the signal coupler (120) as the internal resistance of the insulation monitoring device (100). Based on the composite insulation resistance before correction and the theoretical composite insulation resistance, the signal processor (140) can obtain a calibration factor, which is a factor for error correction. For example, the signal processor (140) can calculate the calibration factor by dividing the theoretical composite insulation resistance by the composite insulation resistance before correction.

[0069] Next, when the signal processor (140) measures the composite insulation resistance after obtaining the calibration factor, it can obtain a corrected composite insulation resistance based on the composite insulation resistance before correction and the calibration factor. In an exemplary embodiment, the signal processor can calculate the corrected composite insulation resistance by multiplying the composite insulation resistance before correction by the calibration factor. The signal processor (140) can provide the corrected composite insulation resistance to determine the insulation status of the power line.

[0071] FIG. 4 is a diagram illustrating the measurement of insulation resistance in an insulation monitoring device according to one embodiment.

[0072] Referring to FIG. 4, the current generated by the test signal applied to the power line by the insulation monitoring device (100) to check the insulation status of the power line can sequentially flow through the first power line (L1), the first insulation resistance (Re1), the second insulation resistance (Re2), the second power line (L2), the signal coupler (120), and the signal detector (130). The magnitude of the voltage drop that occurs when the current passes through the signal detector (130) can be detected as a detection signal (voltage).

[0073] A test signal (applied voltage) can be generated by the signal generator (110) raising the potential. The test signal generated by the signal generator (110) can be applied to the first power line (L1). The current from the test signal can flow to the second power line (L2) through the first insulation resistor (Re1) connecting the first power line (L1) to the ground and the second insulation resistor (Re2) connecting the ground to the second power line (L2).

[0074] At this time, the first insulation resistance (Re1) and the second insulation resistance (Re2) can be connected in parallel, and the combined resistance of the first insulation resistance (Re1) and the second insulation resistance (Re2) can be the combined insulation resistance (Re) representing the insulation state of the entire power line. The current passing through the second power line (L2) can pass through the detection resistance (Rm) constituting the signal detector (130) through the coupler resistance (Rc) constituting the signal coupler (120).

[0075] The potential of the test signal can drop as it passes through the insulation resistance (Re1 and Re2), the coupler resistance (Rc), and the detection resistance (Rm). The magnitude of the potential drop as it passes through the detection resistance (Rm) can be measured by the signal detector (130) as a detection signal (voltage).

[0076] The signal processor (140) is a test signal ( ), detection signal( ), detection resistance( ) and coupler resistor( Based on ), theoretical composite insulation resistance ( ) can be obtained. At this time, composite insulation resistance ( ) and internal resistance( The sum of the values ​​between ) is the detection signal ( It is inversely proportional to ), and the test signal( ) or detection resistor( It can be proportional to ). Theoretical equivalent insulation resistance ( ) can be calculated by the following mathematical formula 1.

[0077] (Mathematical Formula 1)

[0078]

[0079] : Composite insulation resistance

[0080] : Test signal (applied voltage)

[0081] : Detector

[0082] : Detect signal (voltage across the terminals of the detection resistor)

[0083] : Combined resistance of coupler resistance and detector resistance

[0084] : Coupler resistor

[0086] FIG. 5 is a block diagram illustrating a computing environment including a computing device suitable for use as an insulation monitoring device according to one embodiment. In the illustrated embodiment, each component may have different functions and capabilities in addition to those described below, and may include additional components in addition to those described below.

[0087] The illustrated computing environment (10) includes a computing device (12). In one embodiment, the computing device (12) can perform the operation of the insulation monitoring device (100) described in FIGS. 2 to 4.

[0088] The signal generator (110), signal coupler (120), and signal detector (130) of FIG. 2 may correspond to the input / output device (24) of FIG. 5, and the signal processor (140) of FIG. 2 may correspond to the processor (14) of FIG. 5.

[0089] The computing device (12) includes at least one processor (14), a computer-readable storage medium (16), and a communication bus (18). The processor (14) can cause the computing device (12) to operate according to the exemplary embodiment described above. For example, the processor (14) can execute one or more programs stored in the computer-readable storage medium (16). The one or more programs may include one or more computer-executable instructions, and the computer-executable instructions may be configured to cause the computing device (12) to perform operations according to the exemplary embodiment when executed by the processor (14).

[0090] A computer-readable storage medium (16) is configured to store computer-executable instructions or program code, program data and / or other suitable forms of information. A program (20) stored in the computer-readable storage medium (16) includes a set of instructions executable by a processor (14). In one embodiment, the computer-readable storage medium (16) may be memory (volatile memory such as random access memory, non-volatile memory, or a suitable combination thereof), one or more magnetic disk storage devices, optical disk storage devices, flash memory devices, or other forms of storage media that are accessed by a computing device (12) and capable of storing desired information, or a suitable combination thereof.

[0091] The communication bus (18) interconnects various other components of the computing device (12), including the processor (14) and the computer-readable storage medium (16).

[0092] The computing device (12) may also include one or more input / output interfaces (22) and one or more network communication interfaces (26) that provide interfaces for one or more input / output devices (24). The input / output interfaces (22) and network communication interfaces (26) are connected to a communication bus (18). The input / output devices (24) may be connected to other components of the computing device (12) through the input / output interfaces (22). An exemplary input / output device (24) may include an input device such as a pointing device (such as a mouse or trackpad), a keyboard, a touch input device (such as a touchpad or touchscreen), a voice or sound input device, various types of sensor devices and / or imaging devices, and / or an output device such as a display device, a printer, a speaker and / or a network card. An exemplary input / output device (24) may be included inside the computing device (12) as a component constituting the computing device (12), or it may be connected to the computing device (12) as a separate device distinct from the computing device (12).

[0094] Although representative embodiments of the present invention have been described in detail above, those skilled in the art will understand that various modifications can be made to the above-described embodiments without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims set forth below as well as equivalents thereof. Explanation of the symbols

[0096] 20: Power line Re: Insulation resistance among insulation impedances Ce: Insulation capacitor among insulation impedances 100: Insulation monitoring device 110: Signal generator 120: Signal coupler 130: Signal detector 140: Signal processor

Claims

Claim 1 An insulation monitoring device for monitoring the insulation status of one or more power lines, comprising: a signal generator that generates a test signal applied to the one or more power lines; a signal detector that measures a detection signal returning after the test signal passes through the one or more power lines; and a signal coupler comprising one or more coupler resistors, which maintains the insulation monitoring device in an insulated state from the one or more power lines and transmits the test signal that has passed through the one or more power lines to the signal detector. An insulation monitoring device comprising a signal processor that calculates a composite insulation resistance representing the overall insulation state of one or more power lines based on the test signal, the detection signal, and one or more internal resistances constituting the insulation monitoring device, wherein the signal processor obtains a composite insulation resistance before correction based on the test signal, the detection signal, and a detection resistance for measuring the detection signal, obtains a theoretical composite insulation resistance based on the test signal, the detection signal, the detection resistance, and a coupler resistance for receiving the test signal, obtains a calibration factor for correcting a measurement error of the insulation monitoring device based on the composite insulation resistance before correction and the theoretical composite insulation resistance, and, when measuring the composite insulation resistance after obtaining the calibration factor, obtains a corrected composite insulation resistance based on the composite insulation resistance before correction and the calibration factor. Claim 2 delete Claim 3 An insulation monitoring device according to claim 1, wherein the signal processor calculates the calibration factor by dividing the theoretical composite insulation resistance by the composite insulation resistance before correction. Claim 4 delete Claim 5 In claim 1, the signal processor calculates the corrected composite insulation resistance by multiplying the pre-correction composite insulation resistance by the calibration factor, an insulation monitoring device. Claim 6 delete Claim 7 An insulation monitoring device according to claim 1, wherein the signal processor obtains the composite insulation resistance before correction by ignoring the coupler resistance included in the signal coupler, and calculates the theoretical composite insulation resistance by considering the coupler resistance as one of the internal resistances. Claim 8 An insulation monitoring device according to claim 7, wherein each of the one or more coupler resistors is connected in a one-to-one correspondence with the one or more power lines, and the signal detector includes a detection resistor, and the detection signal is a voltage across the ends of the detection resistor when the test signal passes through the power line, the coupler resistor, and the detection resistor. Claim 9 An insulation monitoring device according to claim 8, wherein the sum of the composite insulation resistance and the internal resistance is inversely proportional to the detection signal and proportional to the test signal or the detection resistance. Claim 10 In claim 8, the composite insulation resistance ( ) is an insulation monitoring device calculated by the following mathematical formula 1. (Mathematical Formula 1) : Composite insulation resistance : Test signal (applied voltage) : Detector : Detect signal (voltage across the terminals of the detection resistor) : Combined resistance of coupler resistance and detector resistance : Coupler resistor Claim 11 An insulation monitoring device according to claim 1, wherein each of the one or more power lines maintains an insulating state from the outside by means of an insulation resistance, and each of the insulation resistances is connected in parallel to form a composite insulation resistance, and a decrease in the composite insulation resistance indicates that one or more of the one or more power lines have insulation breakdown. Claim 12 A method of operation of an insulation monitoring device for monitoring the insulation status of one or more power lines, comprising: generating a test signal applied to one or more power lines through a signal generator; maintaining the insulation monitoring device in an insulated state from the one or more power lines through a signal coupler including one or more coupler resistors, and transmitting the test signal that has passed through the one or more power lines to a signal detector; and measuring a detection signal that returns after the test signal has passed through the one or more power lines through the signal detector. A method of operating an insulation monitoring device, comprising the step of calculating a composite insulation resistance representing the overall insulation state of one or more power lines based on the test signal, the detection signal, and one or more internal resistances constituting the insulation monitoring device through a signal processor, wherein the step of calculating the composite insulation resistance includes: obtaining a composite insulation resistance before correction based on the test signal, the detection signal, and a detection resistance for measuring the detection signal; obtaining a theoretical composite insulation resistance based on the test signal, the detection signal, the detection resistance, and a coupler resistance for receiving the test signal; obtaining a calibration factor for correcting a measurement error of the insulation monitoring device based on the composite insulation resistance before correction and the theoretical composite insulation resistance; and, when measuring the composite insulation resistance after obtaining the calibration factor, obtaining a corrected composite insulation resistance based on the composite insulation resistance before correction and the calibration factor. Claim 13 delete Claim 14 A method of operation of an insulation monitoring device according to claim 12, wherein the step of obtaining the calibration factor further comprises the step of calculating the calibration factor by dividing the theoretical composite insulation resistance by the composite insulation resistance before correction. Claim 15 A method of operation of an insulation monitoring device according to claim 12, wherein the composite insulation resistance before correction is obtained by ignoring the coupler resistance included in the signal coupler, and the theoretical composite insulation resistance is obtained by considering the coupler resistance as one of the internal resistances.

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